Need Fastener Engineer Skill Set

[whydontu]

Ok, here’s a question for one of our members who has lots of letters after their name. P.Eng would be good for a start.

I have a project that needs a lot of butterfly valves. Lug butterfly valves have tapped bolt holes in a cast iron or ductile iron body. These valves are sandwiched between pipe flanges, and fastened with hex head bolts from each side.

A very common problem with ham-fisted pipe fitters is they use bolts that are too long, and the bolts contact in the tapped bolt holes. Fitter can’t get the bolts to tighten down to contact the flange face, so they get a cheater bar and give ‘er. This immediately breaks the valve body. Typical failures are stripped bolt holes, a cracked valve body, or in cast iron valves a wedge-shaped chunk of the outer lug breaks off.

So I intend to use full-thread studs from each side, threading in the studs until they touch, then backing off a bit for clearance. Then tighten a nut on the stud to contact the flange face. Like IMG_0196 below, but studs instead of hex head bolts.

My thinking is using studs from each side means even if the studs meet in the tapped bolt holes, tightening the nuts puts the studs in tension and relieving any possible over-loading of the valve body. My unschooled understanding of torque and friction is the friction between the nut and flange face is higher than the friction between the nut and stud, so the torque on the nut is putting a greater percentage of force into stretching the stud rather than forcing the two studs together, unlike using two hex head bolts in contact.

Does this make sense?

 

[David]

Completely uninformed question here: why can’t they be through bolted?

 

[Mike R]

Or, if you can supply studs, why not just supply the right bolts and a few spares so they don't use the wrong ones? My opinion, it probably qualifies as an "engineered" joint (albeit a poor one, also my opinion) when done up as per the manufacture, changing that puts the risk on you so I wouldn't change unless I was 100% sure or the risks due to failure are minimal.

 

[Susquatch]

My thinking is using studs from each side means even if the studs meet in the tapped bolt holes, tightening the nuts puts the studs in tension and relieving any possible over-loading of the valve body. My unschooled understanding of torque and friction is the friction between the nut and flange face is higher than the friction between the nut and stud, so the torque on the nut is putting a greater percentage of force into stretching the stud rather than forcing the two studs together, unlike using two hex head bolts in contact.

Does this make sense?

If I understand (which is questionable), you can't use a through bolt because the center piece is threaded.

I think the question of which part has the most friction depends on their length and diameter. It isn't immediately obvious to me that the nut will turn and the stud won't. And even if it does, what guarantees that this will always be the case?

And what guarantees that each stud will be threaded to the same depth? Ie in the center vs some other point deeper or shallower?

 

[whydontu]

Responses:

Can’t be through bolted, many sections of the piping system need to be removed in service, and a typical section will be a valve > flange x flange pipe spool > valve, and we need to be able to remove the pipe spool without disturbing the valves. Because the valves must remain in place, we can’t just slide the flanged piping off the studs, we have to be able to remove the studs on one side of the valves.

Picture removing the pipe between valve #720 and 70F without undoing any other items or moving the pipes. Piping can flex maybe 1/8” so just enough clearance to pull out the piping spool.

We have 3” and 4” valves, with stainless steel, forged steel, and PVC flanges. These all use 5/8” fasteners, but each flange material is a different thickness. We’d have to use 6 different bolt lengths, and it’s just too dangerous to risk getting bolt lengths mixed up. My intent is to specify the shortest stud length that would work in every possible size/flange combination.

I’m assembling the original piping system, so I can be 100% sure the studs are even. My installation sequence is: hand thread in all the studs on the upstream side of the valve, using a simple template to make sure each stud is imbedded to slightly less than half the valve thickness. Install the valve onto the upstream piping and tighten the nuts to factory torqu spec, making sure the studs don’t turn. Fit up the downstream piping, hand thread in the downstream studs. Back off the downstream studs half a turn or so to provide some clearance between the two studs. (5/8”-11, so half a turn is about 50 thou). Then install the downstream nuts and torque to spec.

The butterfly valves have a protruding rubber seat that seals against the mating pipe flange, so it’s very easy to tell when the valve has been properly torqued. Even if it’s a bit under-torqued it will still seal and function.

 

[van123d]

A couple of thoughts. The original design the bolts can be removed and the valve could be slid between the two flanges. If you have studs sticking out through the flanges it would be trapped and necessitate further disassembly of the system to replace. Not sure if this is an issue or not for you.

The two stud idea relies on the nut slipping on the threads before building sufficient tension force in the casting to break it. This seems reasonable in ideal situations but I would still be concerned about the corner cases. Cross threaded, galling, corrosion, etc.

If you want to go the stud direction could you use a single long stud that protrudes both sides? This would prevent any tension force from being applied to the casting. Appropriate thread locker or pin could be used to prevent the stud from turning. This has its own annoyances as you may need a jam nut to install it or remove it if the stud turns or doesn’t turn when you don’t want it to.

Ultimately I think the original bolt solution makes the most sense. Everything else sounds like a compromise in an attempt to solve fitter training issue.

 

[Susquatch]

@whydontu - I slept on your problem last night. On reflection, I do not think you can guarantee which surface will have the highest friction. There are other variables which inevitably intervene. Minor thread defects among them.

However, I think that stud contact isn't nearly the same situation as bolt contact. When the stud contacts with your nut system the stud compression will always reach a point where the nut will turn instead, and I think that point will always be well below the point at which the valve is damaged. It's not at all the same as a bolt that is too long and gets abused.

What that means for you is that you don't need custom studs, or worry about templates.

The worst that can happen in my view is that the studs could end up being hard to remove.

Could you please do all of us a favour and draw a cross section of this assembly (preferably to scale) so we can assess the stresses involved in damaging the valve in the current bolted condition and compare that to the stresses involved in the stud and nut condition?

Although it's a downright stupid thing to have to create a foolproof design to make up for the errors made by installers, it isn't a lot different from what happens with through threaded T-Nuts on a mill table. Most of us understand that situation quite well. But there is always a new (or old) fellow that doesn't. So it's actually not that hard for me to see how your goons mess this up too.

 

[fixerup]

Like Van123d mention " it's a compromise in an attempt to solve fitter training issue". You can't fix stupid
Were I worked we had vessels with 3 feet diameter flanges and a small 1/8 " dia copper gasket sealing around the perimeter and 60 some bolts to tighten the whole assembly together. It would take hours to put it together to find out it was leaking, all because the assembly technician decided to skip one step in the assembly procedure, which was really easy to follow to have a successful seal.

 

[fixerup]

Whydontu, you are asking for an engineering advise. if in doubt I would get a second opinion just to be safe.

I was asked to seal shut the large flange on the hadronic end cap of the Atlas detector at Cern. This vessel was about 25' in dia with something like 150 bolts and a large omega gasket seal . The engineer asked me to torque it down to X ft/lbs. I asked if there was torque sequence and a gradual torque increase per sequences. He looked at me with a puzzled look and replied NO, just torque to spec. I was somewhat glad because that would of been quite the work out, doing bolt #1 at let say 20 ft/lbs , walk all the way down the scaffold and torque the second bolt #75 to 20 ft/lbs, repeat 150 times going up and down the scafold, all around the flange. Repeat Sequence #2 bolt #1 at 40 ft/lbs ..........etc Sequence #3,4,5 and 6. For large flanges, I like to do multiple sequences to make sure the flange comes in nice, evenly and parallels together. So has a good technician, I followed the procedure exactly has told and did a single torque to spec one bolt at a time going around the perimeter. It leak like a sieve.

 

[Bandit]

In my limited experience, there is going be someone that can screw it up no matter what you do. The problem I see with the stud setup up, is messing up the threads in the valve body, making removing the stud difficult/impossible, by butting 2 stud ends up against each other and giving them a “bit extra”. Many/all? stainless bolts/nuts I have worked with require extra care when installing, clean threads, lubed in many cases, don’t over torque, make sure the nut and bolt will go together the needed amount. Gauling of the threads is a very real problem!
Having different lengths of bolts for different flange materials also invites some problems, it will not tighten up, as is too long, too short and strip the threads when tightening.
Am not sure how to fix the “stupid”, other then going to jail because of the way it was fixed, if found out. Other wise, having a minimum IQ rating on the box doesn’t help either as some can’t read, or will think that is a torque for the bolts/nuts.
If you want a “fun” exercise, tighten up a large link seal, yes they often use stainless bolts, or as @fixerup has posted, very large flanges.
I am not a pipe fitter, but I have delt with this assembly/disassembly problem quite a number of times in past few jobs.

 

[Susquatch]

Could you please do all of us a favour and draw a cross section of this assembly (preferably to scale) so we can assess the stresses involved in damaging the valve in the current bolted condition and compare that to the stresses involved in the stud and nut condition?

@whydontu - although others might benefit from such a drawing, I no longer need it. What you posted earlier was sufficient for my needs.



I left the photo half of this screen shot there for the benefit of others viewing this.

I'll try to explain my assessment in the fewest words I can.

The long bolt is really only a problem because it leaves the bolt head sticking out with a visible gap that installers feel oblidged to eliminate. They can't do that at normal torques so they grunt on it. With no where to go, the threads distort at the entry to the threaded section first and then the distortion progresses down the thread - trying to compress the bolt at the far end most and the near end least. Because the casting cannot distort equally, the casting starts to strip the threads at the near end first or break out (pop) a crater in the center casting around the bolt threads. I think it's somewhat unlikely that the bolt itself would fail.

For non-casting parts, the threads would strip conventionally.

In the stud version, the studs would normally try to pull apart as it is tightened. No big deal and not substantially different than using the proper length of bolt. The main difference not being the stress, but rather surface friction at the threads associated with a turning bolt vs a stationary stud. In both cases, the forces in the threaded area of the stud or bolt are all tension even with contacting studs. The difference is that your goons can see that there is no gap and are more likely to just tighten to spec.

A proper washer under the nut will help ensure that the compressive force distribution in the flange is appropriate.

So ya, I think your stud solution is a good one and it doesn't matter if the ends of the studs are in contact, remain in contact, have a gap to start, or grow one as the nut is tightened. All 4 scenarios are not materially relevant to the final torque required, nor to the performance of the joint.

That's my take at least until someone points out an error in my thinking.

 

[ChazzC]

Ok, here’s a question for one of our members who has lots of letters after their name. P.Eng would be good for a start.

I have a project that needs a lot of butterfly valves. Lug butterfly valves have tapped bolt holes in a cast iron or ductile iron body. These valves are sandwiched between pipe flanges, and fastened with hex head bolts from each side.

A very common problem with ham-fisted pipe fitters is they use bolts that are too long, and the bolts contact in the tapped bolt holes. Fitter can’t get the bolts to tighten down to contact the flange face, so they get a cheater bar and give ‘er. This immediately breaks the valve body. Typical failures are stripped bolt holes, a cracked valve body, or in cast iron valves a wedge-shaped chunk of the outer lug breaks off.

So I intend to use full-thread studs from each side, threading in the studs until they touch, then backing off a bit for clearance. Then tighten a nut on the stud to contact the flange face. Like IMG_0196 below, but studs instead of hex head bolts.

My thinking is using studs from each side means even if the studs meet in the tapped bolt holes, tightening the nuts puts the studs in tension and relieving any possible over-loading of the valve body. My unschooled understanding of torque and friction is the friction between the nut and flange face is higher than the friction between the nut and stud, so the torque on the nut is putting a greater percentage of force into stretching the stud rather than forcing the two studs together, unlike using two hex head bolts in contact.

Does this make sense?

View attachment 61627
View attachment 61628

Or, if you can supply studs, why not just supply the right bolts and a few spares so they don't use the wrong ones? My opinion, it probably qualifies as an "engineered" joint (albeit a poor one, also my opinion) when done up as per the manufacture, changing that puts the risk on you so I wouldn't change unless I was 100% sure or the risks due to failure are minimal.

I agree with @Mike R : the manufacturer's guidance is correct and also allows one side of the assembly being unbolted without disturbing the upstream side of the valve so that a spool on the downstream side can be removed. You need to provide the proper bolts and washers (not shown in the cross-section, but clearly there in the photo, plus good practice so the bolt is not turning against the (potentially) rough/out-of-square surface of the flange.

Supplying the hardware not only eliminates the problem of incorrect length bolts, but also bolts that do not be the required grade.


Not a P.E., but have worked with large piping systems for most of my 40+ years in industry and managed P.E.'s for the last 15 years of that experience.

 

[Chipper5783]

Ok, here’s a question for one of our members who has lots of letters after their name. P.Eng would be good for a start.

I have a project that needs a lot of butterfly valves. Lug butterfly valves have tapped bolt holes in a cast iron or ductile iron body. These valves are sandwiched between pipe flanges, and fastened with hex head bolts from each side.

A very common problem with ham-fisted pipe fitters is they use bolts that are too long, and the bolts contact in the tapped bolt holes. Fitter can’t get the bolts to tighten down to contact the flange face, so they get a cheater bar and give ‘er. This immediately breaks the valve body. Typical failures are stripped bolt holes, a cracked valve body, or in cast iron valves a wedge-shaped chunk of the outer lug breaks off.

So I intend to use full-thread studs from each side, threading in the studs until they touch, then backing off a bit for clearance. Then tighten a nut on the stud to contact the flange face. Like IMG_0196 below, but studs instead of hex head bolts.

My thinking is using studs from each side means even if the studs meet in the tapped bolt holes, tightening the nuts puts the studs in tension and relieving any possible over-loading of the valve body. My unschooled understanding of torque and friction is the friction between the nut and flange face is higher than the friction between the nut and stud, so the torque on the nut is putting a greater percentage of force into stretching the stud rather than forcing the two studs together, unlike using two hex head bolts in contact.

Does this make sense?

I worked many years in a large petro chem plant and bolting of piping is a big deal (referred to as “critical joints”). I have the requisite alphabet soup tacked onto the end of my name - still have a lot to learn.

I am very familiar with the challenge you describe. The various problems identified by other respondents are valid (any solution has its problems). Of course following the manufacturer’s instructions (correct components, clean, suitable prep, all lined up etc) is going to work well. Realistically you are not always going to get that. You already know all that. I think your question is how to improve the likelihood of success, when every is not perfect, recognizing that whatever you propose is not going to solve all scenarios of how to assemble the joint badly (you are not asking that - can’t fix stupid, just trying to make it better).

What you are proposing - a stud in from each side - yes, that is a good solution. I will share some considerations. For the through thread example, you can’t really tell for sure how far the stud is threaded into the valve body (granted you can if you know the stud length, just measure what is protruding) - maybe a stud got swapped. You need to address the condition that the stud on one side is threaded into 90% of the way, so the other is only in 10% (and you can’t see that) - granted you can check with a UT shot (ultrasonic inspection of bolt length - that is a chore). One fix is to notch the stud at about 45% of the valve thickness to about half the thread depth - it does not change the strength and provides a visual indication of the engagement into the valve body.

A second issue is cranking the stud into the valve body - obviously it should go in easy. Though it may not come out easily (as others have pointed out). A couple options here. Certainly the easy option is just to double nut, or a collet threaded stud driver (like from Snapon), you may not always have room for that. So hex the end of the stud for a small wrench (an application for polygon machining, or a wobble broach and make it into a “socket head stud”) - obviously a bit of work, but once set up not a huge deal. Then you can apply the stud in some pretty tight locations.

A point to watch out for is that all wafer valves (especially larger ones) have blind tapped holes. You have to make sure you don’t bind the stud threads in the bottom of the hole - in which case machine the end of the stud into a “button bottom” so there are no threads on the bottom end of the stud (take off about 3 threads).

Yes you can go further, such as drilling a through hole down the stud for getting penetrating oil (help with removing the stud), or drill the stud for a heater (larger studs).

 

[Susquatch]

@whydontu - I feel a need to qualify my earlier comments. I didn't do a PhD on fasteners but I do have a shit ton of professional experience with them. Fasteners play a vital and extensive role in the automotive industry. As I have said before - fastener torque is the leading cause of safety recalls.

BUT - I have virtually no experience or knowledge specific to very large scale piping systems other than factory air, water, steam, and paint distribution systems. I have to defer to you and others on that matter.

Given the pervasive nature of fasteners in our company, we actually had a fasteners division whose job it was to review and approve all fastened connections in all the vehicles we designed and built.

We also routinely consulted with an expert who happened to be in England. Periodically, we would pay to have him visit and give update training to our fastener division.

After I retired, I reached out to him a few times and he gave me personal advice free of charge. He might do that for you too. Sadly, I can't recall his name and I don't seem to have him in my contacts database. You could try googling "Fastener Expert England".

In summary, although I am not an experts expert, I have a pretty good background in fasteners. But I am pretty clueless when it comes to piping. Please use my advice in that context.

 

[KeeponDragon]

while this thread was informative, and has a ton of educated expertise behind it...

I'm still blown away we have a member who was working @ Cern...

that shit's just cool.

 

[whydontu]

Here's a sketch of what I'm doing. I need to be able to remove Pipe 1 without removing Valve 1 or Valve 2. Easy enough if I use hex head bolts, but Pipe 1 can have different flange thicknesses, and a bolt that is suitable for a 1-1/4" thick PVC flange is way too long for a 3/4" thick stainless steel flange. The bolt suitable for the thin flanges only ends up with three or four turns of engagement into the valve body if the valve is mated to a PVC flange. And the operators of this piping system aren't pipe fitters, so there's a very good chance they'll take out the bolts, and then use the same bolts regardless of the composition of the next version of Pipe 1. So I thought of using studs instead. No big deals if the studs are longer than needed, just means a bit of exposed thread at the flange end.

I'm using A193 B7 CrMo studs, heavy flat washers, and A194 2H hex nuts. Universally applicable to the flange materials. (I never thought of using nice big socket set screws, but I've already bought 500 studs so I guess I'm committed.)

I kind of get the impression I'm overthinking this, my curiosity maybe is getting in the way of just completing the project. Even if a stud risks cracking the valve body, the valves and system will still function. Testing of the valves involved taking a display cutaway and installing it in the piping and pressurizing the system to 29 PSIG. No leaks. (German-designed valve, made in Thailand) Photos:

@KeeponDragon , I've never worked at Cern but spent many hours in sewage treatment plants and doing valve repairs in sewage wet wells. Maybe not as prestigious as Cern, but it paid the rent...

 

[KeeponDragon]

@KeeponDragon , I've never worked at Cern but spent many hours in sewage treatment plants and doing valve repairs in sewage wet wells. Maybe not as prestigious as Cern, but it paid the rent...

Meant no disrespect in my comment of @fixerup's work experience...

I'd say your work, in what is definitely not considered as a glamorous place, is just as important...
What you have to work with, no pun intended, can be really shitty.
Chances are, the systems never break down when it's convenient for anyone.
Not to mention, you're working with technology that got its start well over 2000 years ago...in the time of the Romans...
To me, that's just as cool...to see how it's evolved from gravity fed from cisterns on hillsides to being under 100's of psi of forced pressure.
if those engineers then could see what we have now...they'd probably piss themselves.

 

[Susquatch]

Here's a sketch of what I'm doing. I need to be able to remove Pipe 1 without removing Valve 1 or Valve 2.

Again, with almost no piping experience but lots of fastener experience, I think your studs will work just fine.

Whacha using for a torque wrench?

 

[Dan Dubeau]

Personally I think the best solution here is to supply the correct length hardware for each valve. It's the root cause of the problem, so I always prefer to fix it from that angle. Only if that is not available, or if it's unreasonable depending on other variables will I go looking for alternative solutions. Dan Dubeau RSE. (only found out a few weeks ago that I actually have post nominals.....)

With the studs sticking through, subsequent servicing could become a nightmare, as you've now got no clearance to slip anything out because it's stabbed through with the stud. Functionally I think it's fine, and don't see an issue with it holding and performing, it technically solves your problems, but you may be painting yourself in a corner in the future, and I'd hate to be the guy swinging wrenches trying to remove that failed butterfly fiddling around with the studs too. I see a lot of janky stuff at the cement plant, and it's frustrating dealing with the sloppy seconds of another hack that has worked on stuff before. Too lazy to go to stores for the correct bolt to actually thread into the holes, so they through bolt it with smaller and a stack of washers, then caulk it, and spray foam the shit out of it to keep it from leaking....Fun times.....

 

[whydontu]

Meant no disrespect in my comment of @fixerup's work experience...

I'd say your work, in what is definitely not considered as a glamorous place, is just as important...
What you have to work with, no pun intended, can be really shitty.
Chances are, the systems never break down when it's convenient for anyone.
Not to mention, you're working with technology that got its start well over 2000 years ago...in the time of the Romans...
To me, that's just as cool...to see how it's evolved from gravity fed from cisterns on hillsides to being under 100's of psi of forced pressure.
if those engineers then could see what we have now...they'd probably piss themselves.

I doubt they'd be too surprised. An early Roman plug valve vs. one I could take off the shelf tomorrow. The Roman engineer would completely understand how today's valve works, and the only new aspect would be threaded ends, and even then the Roman engineer would only be interested in how you cut the threads. The Roman engineer might be surprised by electronics, but likely just as baffled why we still have wars.